While they were not more likely than children with normal sodium to need mechanical ventilation, they were more than twice as likely to need noninvasive breathing support, Luu and colleagues reported online in the Journal of Pediatrics.

The findings, from a single-institution chart review, are surprising because few of the children had severe hyponatremia, Luu and colleagues noted.

But "we did not anticipate that even mild hyponatremia would be related to worse clinical outcomes in our study group," Luu and colleagues wrote.

The researchers looked at clinical outcomes for 102 children with bronchiolitis, ages 1 month to 2 years, admitted to pediatric intensive care at Children's Hospital Colorado over a 26-month period.

Using the standard definition, 23 patients had hyponatremia at the time of admission or within the first 2 hours, but only one had severe hyponatremia, defined as less than 125 mEq/L.

Nevertheless, Luu and colleagues found that mortality was significantly higher in the hyponatremic group at 13% versus 0% for those without hyponatremia (P=0.011).

The average time on mechanical ventilator was 8.4 days for those with low sodium compared with 4.1 days for those without (P=0.001), although the former were not at greater risk of needing mechanical ventilation.

Average duration of stay in the ICU was 10.63 days for the hyponatremic children and 5.82 days for the others (P=0.007).

Finally, 65% of the children with low sodium needed noninvasive ventilator support, compared with 24% of those with normal sodium (P=0.007).

The authors reported that there were no differences in the number of patients with seizures, bronchodilator use, steroid use, intubation requirement, oxygen use at discharge, or hospital readmission.

Luu and colleagues cautioned that the study was retrospective and therefore cannot claim cause and effect.

Importantly, the study could not take into account fluid administration during the first 24 hours of admission, which "could have considerable influence on a variety of the studied outcomes," they pointed out.

They also were unable to take into account pre-ICU administration of hypotonic fluids, which might have affected the incidence of hyponatremia.

Nevertheless, Luu and colleagues concluded, the finding is sufficiently concerning that "a prospective study to evaluate the effects of hyponatremia appears justified."

The authors did not report any external support for the study or any potential conflicts of interest.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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